The invention relates to a method of controlling the process of spinning-in yarn in units of open-end spinning machines as well as to an apparatus for carrying out the method.
The heretofore known processes of automatically controlling the yarn spinning-in in open-end spinning machines have been performed by means of automatic service units operating in a spinning-in cycle preadjusted or programmed for a given yarn count, wherein at the start of the spinning rotor a controlled spinning-in process takes place, in which the take-off speed of yarn to be spun-in is governed by an increasing speed of revolution of the spinning rotor while the sliver supply speed corresponds to the yarn take-off speed (West-German Published Patent Application Nos. 2,321,775 and 3,144,760); alternatively, the sliver supply speed is regulated according to the entire yarn draft predetermined for the spinning process (West-German Publ. patent application No. 3,144,761), or the complete spinning-in process is controlled by means of complicated controlling elements which are designed for recording various quantities picked up during the start of the spinning rotor whereupon on the basis thereof yarn is returned into the rotor for being spun-in (West-german Publ. patent application No. 3,144,776).
However, any correct adjustment of the spinning-in cycle for a given yarn count in an automatic service device traveling along the spinning units of the machine, or in individual automatic units operating in each of the spinning station, is a rather complicated procedure since the spinning-in process depends on a plurality of variable quantities, and because of the fact that, due to various characteristics of textile materials, there does
not yet exist and probably will never be found an exact mathematic model that would enable such a cycle to be calculated. For this reason, the spinning-in cycle by which the sequence of operations of the central automatic service unit or the individual service devices is determined is adjusted empirically, depending upon the operator's experience according to the type of fibrous material processed on a selected spinning station of the machine.
Even if the spinning-in cycle in the respective spinning unit is satisfactorily adjusted, a different quality of splice spots occurs in the other stations. This is caused by tolerances in the manufacture of individual elements of the spinning units by the wear of differentially stressed parts thereof, by different thrusts of the driving belts or the like. By this, of course, also dynamic characteristics of the individual spinning units vary during the spinning-in process, which results not only in a considerably wide spectrum of appearance and strength values of the yarn splice spots but also in an unreliability of the spinning-in process itself which has to be repeated several times, especially in the cases wherein the dynamic characteristics of spinning units vary excessively.
In the spinning-in process it is necessary to be relatively precise in determining some spinning-in parameters. One such parameter is the length of yarn to be returned from an initial position to the collecting groove of the spinning rotor, this length having to be determined before the start of the spinning-in process. To obtain a splice joint of high quality, a relatively precise yarn length has to be deposited onto the fibrous ribbon in the collecting groove of the spinning rotor.
This yarn length spinning-in parameter has hitherto been determined experimentally by the operator and the thus ascertained value has been adjusted or set up in a service unit. There are a number of known types of such service units, wherein the yarn length to be returned, or the adjustment thereof, is effected either by timing elements, or by means of a cam and adjustable switches (cf. Brit. Pat. 1,458,435), or by means of pulse counters (cf. U.S. Pat. No. 4,102,116 or 4,033,107).
Once adjusted, the yarn length spinning-in parameter can be modified, either by the operator, or automatically, in dependence on actually ascertained values within the scope of certain tolerances (cf. DE-OS No. 29 44 219=CS 210,059). Such a measure has been characterized in that it has respected some manufacturing tolerances, wear of variously stressed parts of spinning units, which means that various dynamic properties of spinning units and their changes have been taken into account.
As hereinabove set forth, this yarn length spinning-in parameter has had, however, to be ascertained preliminarily and experimentally. Such an adjustment or determination of this parameter is relatively time-consuming and therefore disadvantageous, particularly in those cases where changes of yarn count (in tex) and/or rotor diameter in the machine frequently occur. Apart from this, such a method is, owing to the splice joint quality, inaccurate and has to be modified by means of a control device and respective tuning elements provided in the automatic service unit.
In spinning-in process it is also necessary to be relatively precise in determining the amount of fibers to be supplied into the spinning rotor in order to obtain a desired quality of splice joint. As known from the British Patent Specification No. 1,458,435, the instant of starting the fiber supply to the spinning rotor since the start of spinning-in process is determined by time metering means whose values are adjustable. In this way, the fiber supply period up to the yarn take-off instant can be set up. This time period which is called the fiber supply spinning-in parameter, gives the fiber amount to be supplied to the spinning rotor up to the yarn take-off start in order to produce a fibrous ribbon in the collecting groove of the spinning rotor, onto which the yarn end is to be deposited in the spinning-in process. This time period must always be predetermined and set up in the corresponding electrical circuit of the spinning-in mechanism. This period has hitherto been ascertained experimentally for every yarn count (in tex), which means that a presupposed value has been set up, and after the inspection of splice joint quality, the set up value has been corrected, if necessary.
According to the German DE-OS No. 2,944,219, a value set up in a time program is compared with a value actually ascertained in a comparing element 7 whereupon the set up values are corrected by a correcting element 4 with respect to correction values defining the admissible time tolerances. Thus, the differences between the actual value and the set up value are corrected either by the operator, or automatically, but always within the range of tolerance limits. This means that it is always necessary to determine the fiber supply spinning-in parameter with regard to the yarn count (in tex) and the spinning rotor diameter, which is disadvantageous, particularly with machines where spinning rotors are frequently exchanged for other ones with different diameters, with regard to the character of fibers to be processed, or where the yarn count is frequently changed.
As disclosed in the U.S. Pat. No. 4,178,749, the splice joint quality, after a programmed spinning-in process, is inspected and evaluated, and in case of an objectionable value, an intentional breakage is effected and the programmed spinning-in process is repeated. The patent does not solve and does not predetermine the fiber supply spinning-in parameter, either. Yet, in this case as well, this parameter has to be predetermined and stored into the program.
Thus it is necessary for carrying out the known spinning processes that the operator may know such a primary or initial adjustment of an automatic service unit, in order to obtain a splice joint at all, although its quality may be questionable. This means that the first adjustment of the automatic service has to be either estimated or effected according to experience, which, with a considerable variability of fibrous material properties in view, is troublesome. It is particularly the determination of the fiber supply spinning-parameter where other processes, such as final combing-out of fibers from fibrous beard by the opening cylinder even after stopping the fiber supply, play their part, that is relatively time-consuming.
According to Czechoslovak Inventor's Certificate No. 210,059, it has been proposed to equip the driving means of spinning stations with adjusting elements for tuning each of the spinning stations up to a desired level. For the time being, however, the installation of such means is too expensive and, apart from this, the operation thereof requires the intervention of the operator who will thereby lose a part of his work capacity.